Power conversion apparatus and method for starting up the same

ABSTRACT

A power conversion apparatus includes a transformer; a primary side full bridge circuit provided on a primary side of the transformer; a first port connected to the primary side full bridge circuit; a second port connected to a center tap of the primary side of the transformer; a secondary side full bridge circuit provided on a secondary side of the transformer; a third port connected to the secondary side full bridge circuit; and a control unit configured to cause an upper arm of the secondary side full bridge circuit to operate in an active region in a case where a capacitor connected to the third port is charged with a transmitted power transmitted to the secondary side full bridge circuit via the transformer from the primary side full bridge circuit when power of the second port is stepped up and the stepped up power is output to the first port.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2014-048199 filed onMar. 11, 2014 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for converting powerbetween a plurality of ports.

2. Description of Related Art

A power conversion apparatus for converting power between a plurality ofinput/output ports is known (see Japanese Patent Application PublicationNo. 2011-193713 (JP 2011-193713 A), for example). A capacitor isconnected to at least one port in the power conversion apparatus.

However, if a power supply is connected to the port in a state where thecapacitor that is connected to the port is almost not charged, there isa possibility that an inrush current flowing to the capacitor becomesexcessive.

SUMMARY OF THE INVENTION

Therefore, the present invention provides a power conversion apparatusand a method for starting up the same which enable to suppress an inrushcurrent flowing to a capacitor that is connected to a port.

According to one aspect of the present invention, there is provided apower conversion apparatus including: a transformer; a primary side fullbridge circuit that is provided on a primary side of the transformer; afirst port that is connected to the primary side full bridge circuit; asecond port that is connected to a center tap of the primary side of thetransformer; a secondary side full bridge circuit that is provided on asecondary side of the transformer; a third port that is connected to thesecondary side full bridge circuit; and a control unit that isconfigured to cause an upper arm of the secondary side full bridgecircuit to operate in an active region in a case where a capacitor thatis connected to the third port is charged with a transmitted power thatis transmitted to the secondary side full bridge circuit via thetransformer from the primary side full bridge circuit when a power ofthe second port is stepped up and the stepped up power is output to thefirst port.

According to one embodiment, it is capable of suppressing an inrushcurrent flowing to a capacitor that is connected to a port.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a diagram showing an example of a configuration of a powerconversion apparatus;

FIG. 2 is a diagram showing an example of a configuration of a controlunit;

FIG. 3 is a timing chart showing an example of switching operations of aprimary side circuit and a secondary side circuit;

FIG. 4 is a flowchart showing an example of a method for starting up thepower conversion apparatus;

FIG. 5 is a timing chart showing an example of operations of the powerconversion apparatus when it is started up;

FIG. 6 is a diagram showing an example of a direction and a path of acurrent charging a capacitor by an arrow;

FIG. 7 is a diagram showing an example of a direction and a path of thecurrent charging the capacitor by an arrow;

FIG. 8 is a diagram showing an example of a direction and a path of thecurrent charging the capacitor by an arrow;

FIG. 9 is a timing chart showing an example of a duty ratio thatgradually increases;

FIG. 10 is a diagram showing an example of a structure in which diodesof an upper arm are disposed oppositely;

FIG. 11 is a diagram showing an example of a structure in which diodesof a lower arm are disposed oppositely; and

FIG. 12 is a timing chart showing an example in which an operation of anarm in an active region is interrupted.

DETAILED DESCRIPTION OF EMBODIMENTS

<Configuration of Power Supply Apparatus 101>

FIG. 1 is a block diagram showing an example of a configuration of apower supply apparatus 101 which is an embodiment of a power conversionapparatus. For example, the power supply apparatus 101 is a power supplysystem that includes a power supply circuit 10, a control unit 50 and asensor unit 70. For example, the power supply apparatus 101 is a systemthat is mounted on a vehicle such as an automobile, and distributespower to various loads of the vehicle. A hybrid vehicle, a plug-inhybrid vehicle, an electric vehicle, and so on may be cited as specificexamples of this vehicle. The power supply apparatus 101 may also bemounted on a vehicle using an engine as a driving source.

For example, the power supply apparatus 101 includes, as primary sideports, a first input/output port 60 a to which a primary side highvoltage system load 61 a is connected and a second input/output port 60c to which a primary side low voltage system load 61 c and a primaryside low voltage system power supply 62 c are connected. The primaryside low voltage system power supply 62 c supplies power to the primaryside low voltage system load 61 c, which is operated by an identicalvoltage system (a 12 V system, for example) to the primary side lowvoltage system power supply 62 c. Further, the primary side low voltagesystem power supply 62 c supplies power stepped up by a primary sideconversion circuit 20 provided in the power supply circuit 10 to theprimary side high voltage system load 61 a, for example, which isoperated by a different voltage system (a higher 48 V system than the 12V system, for example) to the primary side low voltage system powersupply 62 c. A secondary battery such as a lead battery may be cited asa specific example of the primary side low voltage system power supply62 c.

For example, the power supply apparatus 101 includes, as secondary sideports, a third input/output port 60 b to which a secondary side highvoltage system load 61 b and a secondary side high voltage system powersupply 62 b are connected and a fourth input/output port 60 d to which asecondary side low voltage system load 61 d and a secondary side lowvoltage system power supply 62 d are connected. The secondary side highvoltage system power supply 62 b supplies power to the secondary sidehigh voltage system load 61 b, which is operated by an identical voltagesystem (a higher 288 V system than the 12 V system and the 48 V system,for example) to the secondary side high voltage system power supply 62b. Further, the secondary side high voltage system power supply 62 bsupplies power stepped down by a secondary side conversion circuit 30provided in the power supply circuit 10 to the secondary side lowvoltage system load 61 d, for example, which is operated by a differentvoltage system (a lower 72 V system than the 288 V system, for example)to the secondary side high voltage system power supply 62 b. A secondarybattery such as a lithium ion battery may be cited as a specific exampleof the secondary side high voltage system power supply 62 b.

The secondary side low voltage system power supply 62 d supplies powerto the secondary side low voltage system load 61 d, which is operated byan identical voltage system (the 72 V system, for example) to thesecondary side low voltage system power supply 62 d. Further, thesecondary side low voltage system power supply 62 d supplies powerstepped up by the secondary side conversion circuit 30 provided in thepower supply circuit 10 to the secondary side high voltage system load61 b, for example, which is operated by a higher voltage system (the 288V system, for example) than the secondary side low voltage system powersupply 62 d. A solar power supply (a solar power generator), an AC-DCconverter for converting a commercial AC power into a DC power, asecondary battery and so on may be cited as a specific example of thesecondary side low voltage system power supply 62 d.

The power supply circuit 10 is a power conversion circuit that includesthe four input/output ports described above and has functions forselecting any two input/output ports from the four input/output portsand performing power conversion between the two input/output ports.Further, the power supply apparatus 101 including the power supplycircuit 10 may be an apparatus that includes a plurality of, at leastthree, input/output ports, and is capable of converting power betweenany two input/output ports from the plurality of, at least three,input/output ports. For example, the power supply circuit 10 may also bea circuit that has three input/output ports without the fourthinput/output port 60 d.

Port powers Pa, Pc, Pb, Pd are input/output powers (input powers oroutput powers) of the first input/output port 60 a, the secondinput/output port 60 c, the third input/output port 60 b, and the fourthinput/output port 60 d, respectively. Port voltages Va, Vc, Vb, Vd areinput/output voltages (input voltages or output voltages) of the firstinput/output port 60 a, the second input/output port 60 c, the thirdinput/output port 60 b, and the fourth input/output port 60 d,respectively. Port currents Ia, Ic, Ib, Id are input/output currents(input currents or output currents) of the first input/output port 60 a,the second input/output port 60 c, the third input/output port 60 b, andthe fourth input/output port 60 d, respectively.

The power supply circuit 10 includes a capacitor Cl that is provided toconnect to the first input/output port 60 a, a capacitor C3 that isprovided to connect to the second input/output port 60 c, a capacitor C2that is provided to connect to the third input/output port 60 b, and acapacitor C4 that is provided to connect to the fourth input/output port60 d. Film capacitors, aluminum electrolytic capacitors, ceramiccapacitors, polymer electrolytic capacitors, and so on may be cited asspecific examples of the capacitors Cl, C2, C3, C4.

The capacitor Cl is inserted between a high potential side terminal 613of the first input/output port 60 a and a low potential side terminal614 of the first input/output port 60 a and the second input/output port60 c. The capacitor C3 is inserted between a high potential sideterminal 616 of the second input/output port 60 c and the low potentialside terminal 614 of the first input/output port 60 a and the secondinput/output port 60 c. The capacitor C2 is inserted between a highpotential side terminal 618 of the third input/output port 60 b and alow potential side terminal 620 of the third input/output port 60 b andthe fourth input/output port 60 d. The capacitor C4 is inserted betweena high potential side terminal 622 of the fourth input/output port 60 dand the low potential side terminal 620 of the third input/output port60 b and the fourth input/output port 60 d.

The capacitors C1, C2, C3, C4 may be provided either inside or outsidethe power supply circuit 10.

The power supply circuit 10 is a power conversion circuit configured toinclude the primary side conversion circuit 20 and the secondary sideconversion circuit 30. Further, the primary side conversion circuit 20and the secondary side conversion circuit 30 are connected via a primaryside magnetic coupling reactor 204 and a secondary side magneticcoupling reactor 304, and magnetically coupled by a transformer 400 (acenter tapped transformer). The primary side ports configured of thefirst input/output port 60 a and the second input/output port 60 c andthe secondary side ports configured of the third input/output port 60 band the fourth input/output port 60 d are connected via the transformer400.

The primary side conversion circuit 20 is a primary side circuitconfigured to include a primary side full bridge circuit 200, the firstinput/output port 60 a, and the second input/output port 60 c. Theprimary side full bridge circuit 200 is provided on a primary side ofthe transformer 400. The primary side full bridge circuit 200 is aprimary side power conversion unit configured to include a primary sidecoil 202 of the transformer 400, the primary side magnetic couplingreactor 204, a primary side first upper arm U1, a primary side firstlower arm /U1, a primary side second upper arm V1, and a primary sidesecond lower arm /V1. Here, the primary side first upper arm U1, theprimary side first lower arm /U1, the primary side second upper arm V1,and the primary side second lower arm /V1 are constituted by switchingelements respectively configured to include, for example, an N channeltype metal oxide semiconductor field effect transistor (MOSFET) and abody diode (a parasitic diode) serving as a parasitic element of theMOSFET. Additional diodes may be connected to the MOSFET in parallel.Diodes 81, 82, 83, 84 are illustrated in FIG. 1.

The primary side full bridge circuit 200 includes a primary sidepositive electrode bus line 298 connected to the high potential sideterminal 613 of the first input/output port 60 a, and a primary sidenegative electrode bus line 299 connected to the low potential sideterminal 614 of the first input/output port 60 a and the secondinput/output port 60 c.

A primary side first arm circuit 207 connecting the primary side firstupper arm U1 and the primary side first lower arm /U1 in series isattached between the primary side positive electrode bus line 298 andthe primary side negative electrode bus line 299. The primary side firstarm circuit 207 is a primary side first power conversion circuit unit (aprimary side U phase power conversion circuit unit) capable ofperforming a power conversion operation by switching the primary sidefirst upper arm U1 and the primary side first lower arm /U1 ON and OFF.Further, a primary side second arm circuit 211 connecting the primaryside second upper arm V1 and the primary side second lower arm /V1 inseries is attached between the primary side positive electrode bus line298 and the primary side negative electrode bus line 299 in parallelwith the primary side first arm circuit 207. The primary side second armcircuit 211 is a primary side second power conversion circuit unit (aprimary side V phase power conversion circuit unit) capable ofperforming a power conversion operation by switching the primary sidesecond upper arm V1 and the primary side second lower arm /V1 ON andOFF.

The primary side coil 202 and the primary side magnetic coupling reactor204 are provided in a bridge part connecting a midpoint 207 m of theprimary side first arm circuit 207 to a midpoint 211 m of the primaryside second arm circuit 211. To describe connection relationships to thebridge part in more detail, one end of a primary side first reactor 204a of the primary side magnetic coupling reactor 204 is connected to themidpoint 207 m of the primary side first arm circuit 207, and one end ofthe primary side coil 202 is connected to another end of the primaryside first reactor 204 a. Further, one end of a primary side secondreactor 204 b of the primary side magnetic coupling reactor 204 isconnected to another end of the primary side coil 202, and another endof the primary side second reactor 204 b is connected to the midpoint211 m of the primary side second arm circuit 211. Note that the primaryside magnetic coupling reactor 204 is configured to include the primaryside first reactor 204 a and the primary side second reactor 204 b,which is magnetically coupled to the primary side first reactor 204 a bya coupling coefficient k₁.

The midpoint 207 m is a primary side first intermediate node between theprimary side first upper arm U1 and the primary side first lower arm/U1, and the midpoint 211 m is a primary side second intermediate nodebetween the primary side second upper arm V1 and the primary side secondlower arm /V1.

The first input/output port 60 a is a port which is connected to theprimary side full bridge circuit 200 and is provided between the primaryside positive electrode bus line 298 and the primary side negativeelectrode bus line 299. The first input/output port 60 a is configuredto include the terminal 613 and the terminal 614. The secondinput/output port 60 c is a port which is connected to a center tap 202m of the primary side of the transformer 400 and is provided between theprimary side negative electrode bus line 299 and the center tap 202 m ofthe primary side coil 202. The second input/output port 60 c isconfigured to include the terminal 614 and the terminal 616.

The center tap 202 m is connected to the high potential side terminal616 of the second input/output port 60 c. The center tap 202 m is anintermediate connection point between a primary side first winding 202 aand a primary side second winding 202 b constituting the primary sidecoil 202.

The secondary side conversion circuit 30 is a secondary side circuitconfigured to include a secondary side full bridge circuit 300, thethird input/output port 60 b, and the fourth input/output port 60 d. Thesecondary side full bridge circuit 300 is provided on a secondary sideof the transformer 400. The secondary side full bridge circuit 300 is asecondary side power conversion unit configured to include a secondaryside coil 302 of the transformer 400, the secondary side magneticcoupling reactor 304, a secondary side first upper arm U2, a secondaryside first lower arm /U2, a secondary side second upper arm V2, and asecondary side second lower arm /V2. Here, the secondary side firstupper arm U2, the secondary side first lower arm /U2, the secondary sidesecond upper arm V2, and the secondary side second lower arm /V2 areconstituted by switching elements respectively configured to include,for example, an N channel type MOSFET and a body diode (a parasiticdiode) serving as a parasitic element of the MOSFET. Additional diodesmay be connected to the MOSFET in parallel. Diodes 85, 86, 87, 88 areillustrated in FIG. 1.

The secondary side full bridge circuit 300 includes a secondary sidepositive electrode bus line 398 connected to the high potential sideterminal 618 of the third input/output port 60 b, and a secondary sidenegative electrode bus line 399 connected to the low potential sideterminal 620 of the third input/output port 60 b and the fourthinput/output port 60 d.

A secondary side first arm circuit 307 connecting the secondary sidefirst upper arm U2 and the secondary side first lower arm /U2 in seriesis attached between the secondary side positive electrode bus line 398and the secondary side negative electrode bus line 399. The secondaryside first arm circuit 307 is a secondary side first power conversioncircuit unit (a secondary side U phase power conversion circuit unit)capable of performing a power conversion operation by switching thesecondary side first upper arm U2 and the secondary side first lower arm/U2 ON and OFF. Further, a secondary side second arm circuit 311connecting the secondary side second upper arm V2 and the secondary sidesecond lower arm /V2 in series is attached between the secondary sidepositive electrode bus line 398 and the secondary side negativeelectrode bus line 399 in parallel with the secondary side first armcircuit 307. The secondary side second arm circuit 311 is a secondaryside second power conversion circuit unit (a secondary side V phasepower conversion circuit unit) capable of performing a power conversionoperation by switching the secondary side second upper arm V2 and thesecondary side second lower arm /V2 ON and OFF.

The secondary side coil 302 and the secondary side magnetic couplingreactor 304 are provided in a bridge part connecting a midpoint 307 m ofthe secondary side first arm circuit 307 to a midpoint 311 m of thesecondary side second arm circuit 311. To describe connectionrelationships to the bridge part in more detail, one end of a secondaryside first reactor 304 a of the secondary side magnetic coupling reactor304 is connected to the midpoint 307 m of the secondary side first armcircuit 307, and one end of the secondary side coil 302 is connected toanother end of the secondary side first reactor 304 a. Further, one endof a secondary side second reactor 304 b of the secondary side magneticcoupling reactor 304 is connected to another end of the secondary sidecoil 302, and another end of the secondary side second reactor 304 b isconnected to the midpoint 311 m of the secondary side second arm circuit311. Note that the secondary side magnetic coupling reactor 304 isconfigured to include the secondary side first reactor 304 a and thesecondary side second reactor 304 b, which is magnetically coupled tothe secondary side first reactor 304 a by a coupling coefficient k₂.

The midpoint 307 m is a secondary side first intermediate node betweenthe secondary side first upper arm U2 and the secondary side first lowerarm /U2, and the midpoint 311 m is a secondary side second intermediatenode between the secondary side second upper arm V2 and the secondaryside second lower arm /V2.

The third input/output port 60 b is a port which is connected to thesecondary side full bridge circuit 300 and is provided between thesecondary side positive electrode bus line 398 and the secondary sidenegative electrode bus line 399. The third input/output port 60 b isconfigured to include the terminal 618 and the terminal 620. The fourthinput/output port 60 d is a port which is connected to a center tap 302m of the secondary side of the transformer 400 and is provided betweenthe secondary side negative electrode bus line 399 and the center tap302 m of the secondary side coil 302. The fourth input/output port 60 dis configured to include the terminal 620 and the terminal 622.

The center tap 302 m is connected to the high potential side terminal622 of the fourth input/output port 60 d. The center tap 302 m is anintermediate connection point between a secondary side first winding 302a and a secondary side second winding 302 b constituting the secondaryside coil 302.

In FIG. 1, the power supply apparatus 101 includes the sensor unit 70.The sensor unit 70 serves as detecting means that detects aninput/output value Y of at least one of the first to fourth input/outputports 60 a, 60 c, 60 b, 60 d at predetermined detection period intervalsand outputs a detection value Yd corresponding to the detectedinput/output value Y to the control unit 50. The detection value Yd maybe a detected voltage obtained by detecting the input/output voltage, adetected current obtained by detecting the input/output current, or adetected power obtained by detecting the input/output power. The sensorunit 70 may be provided either inside or outside the power supplycircuit 10.

The sensor unit 70 includes, for example, a voltage detection unit thatdetects the input/output voltage generated in at least one of the firstto fourth input/output ports 60 a, 60 c, 60 b, 60 d. For example, thesensor unit 70 includes a primary side voltage detection unit thatoutputs at least one detected voltage from among an input/output voltageVa and an input/output voltage Vc as a primary side voltage detectionvalue, and a secondary side voltage detection unit that outputs at leastone detected voltage from among an input/output voltage Vb and aninput/output voltage Vd as a secondary side voltage detection value.

The voltage detection unit of the sensor unit 70 includes, for example,a voltage sensor that monitors an input/output voltage value of at leastone port, and a voltage detection circuit that outputs a detectedvoltage corresponding to the input/output voltage value monitored by thevoltage sensor to the control unit 50.

The sensor unit 70 includes, for example, a current detection unit thatdetects the input/output current flowing through at least one of thefirst to fourth input/output ports 60 a, 60 c, 60 b, 60 d. For example,the sensor unit 70 includes a primary side current detection unit thatoutputs at least one detected current from among an input/output currentIa and an input/output current Ic as a primary side current detectionvalue, and a secondary side current detection unit that outputs at leastone detected current from among an input/output current Ib and aninput/output current Id as a secondary side current detection value.

The current detection unit of the sensor unit 70 includes, for example,a current sensor that monitors an input/output current value of at leastone port, and a current detection circuit that outputs a detectedcurrent corresponding to the input/output current value monitored by thecurrent sensor to the control unit 50.

The power supply apparatus 101 includes the control unit 50. Forexample, the control unit 50 is an electronic circuit that includes amicrocomputer having an inbuilt central processing unit (CPU). Thecontrol unit 50 may be provided either inside or outside the powersupply circuit 10.

The control unit 50 feedback-controls a power conversion operationperformed by the power supply circuit 10 such that the detected value Ydof the input/output value Y of at least one of the first to fourthinput/output ports 60 a, 60 c, 60 b, 60 d converges to a target value Yoset in the port. For example, the target value Yo is a command value setby the control unit 50 or a predetermined apparatus other than thecontrol unit 50 on the basis of driving conditions defined in relationto the respective loads (the primary side low voltage system load 61 cand so on, for example) connected to the input/output ports. The targetvalue Yo functions as an output target value when power is output fromthe port and an input target value when power is input into the port,and may be a target voltage value, a target current value, or a targetpower value.

Further, the control unit 50 feedback-controls the power conversionoperation performed by the power supply circuit 10 such that atransmitted power P transmitted between the primary side conversioncircuit 20 and the secondary side conversion circuit 30 via thetransformer 400 converges to a set target transmitted power Po. Thetransmitted power will also be referred to as power transmission amount.The target transmitted power will also be referred to as commandtransmitted power.

The control unit 50 feedback-controls the power conversion operationperformed by the power supply circuit 10 by varying a value of apredetermined control parameter X, and is thus capable of adjusting therespective input/output values Y of the first to fourth input/outputports 60 a, 60 c, 60 b, 60 d of the power supply circuit 10. Two controlvariables, namely a phase difference φ and a duty ratio D (an ON time δ)are used as the main control parameters X.

The phase difference φ is a deviation (a time lag) between switchingtimings of identical-phase power conversion circuit units of the primaryside full bridge circuit 200 and the secondary side full bridge circuit300. The duty ratio D (the ON time δ) is a duty ratio (an ON time)between switching waveforms of the respective power conversion circuitunits constituting the primary side full bridge circuit 200 and thesecondary side full bridge circuit 300.

The two control parameters X can be controlled independently of eachother. The control unit 50 varies the input/output values Y of therespective input/output ports of the power supply circuit 10 byperforming duty ratio control and/or phase control on the primary sidefull bridge circuit 200 and the secondary side full bridge circuit 300using the phase difference φ and the duty ratio D (the ON time δ).

FIG. 2 is a block diagram of the control unit 50. The control unit 50 isa control unit having a function for performing switching control on therespective switching elements of the primary side conversion circuit 20,such as the primary side first upper arm U1, and the respectiveswitching elements of the secondary side conversion circuit 30, such asthe secondary side first upper arm U2. The control unit 50 is configuredto include a power conversion mode determination processing unit 502, aphase difference φ determination processing unit 504, an ON time δdetermination processing unit 506, a primary side switching processingunit 508, and a secondary side switching processing unit 510. Forexample, the control unit 50 is an electronic circuit that includes amicrocomputer having an inbuilt CPU.

For example, the power conversion mode determination processing unit 502selects and sets an operating mode from among power conversion modes Ato L of the power supply circuit 10, to be described below, on the basisof a predetermined external signal (for example, a signal indicating thedeviation between the detected value Yd and the target value Yo in oneof the ports). As regards the power conversion modes, in mode A, powerinput from the first input/output port 60 a is converted and output tothe second input/output port 60 c. In mode B, power input from the firstinput/output port 60 a is converted and output to the third input/outputport 60 b. In mode C, power input from the first input/output port 60 ais converted and output to the fourth input/output port 60 d.

In mode D, power input from the second input/output port 60 c isconverted and output to the first input/output port 60 a. In mode E,power input from the second input/output port 60 c is converted andoutput to the third input/output port 60 b. In mode F, power input fromthe second input/output port 60 c is converted and output to the fourthinput/output port 60 d.

In mode G, power input from the third input/output port 60 b isconverted and output to the first input/output port 60 a. In mode H,power input from the third input/output port 60 b is converted andoutput to the second input/output port 60 c. In mode I, power input fromthe third input/output port 60 b is converted and output to the fourthinput/output port 60 d.

In mode J, power input from the fourth input/output port 60 d isconverted and output to the first input/output port 60 a. In mode K,power input from the fourth input/output port 60 d is converted andoutput to the second input/output port 60 c. In mode L, power input fromthe fourth input/output port 60 d is converted and output to the thirdinput/output port 60 b.

The phase difference φ determination processing unit 504 has a functionfor setting a phase difference φ between switching period motions of theswitching elements between the primary side conversion circuit 20 andthe secondary side conversion circuit 30 in order to cause the powersupply circuit 10 to function as a direct current-direct current (DC-DC)converter circuit.

The ON time δ determination processing unit 506 has a function forsetting an ON time δ of the switching elements of the primary sideconversion circuit 20 and the secondary side conversion circuit 30 inorder to cause the primary side conversion circuit 20 and the secondaryside conversion circuit 30 to function respectively as step-up/step-downcircuits.

The primary side switching processing unit 508 has a function forperforming switching control on the respective switching elementsconstituted by the primary side first upper arm U1, the primary sidefirst lower arm /U1, the primary side second upper arm V1, and theprimary side second lower arm N1, on the basis of outputs of the powerconversion mode determination processing unit 502, the phase differenceφ determination processing unit 504, and the ON time δ determinationprocessing unit 506.

The secondary side switching processing unit 510 has a function forperforming switching control on the respective switching elementsconstituted by the secondary side first upper arm U2, the secondary sidefirst lower arm /U2, the secondary side second upper arm V2, and thesecondary side second lower arm /V2, on the basis of the outputs of thepower conversion mode determination processing unit 502, the phasedifference φ determination processing unit 504, and the ON time δdetermination processing unit 506.

<Operation of Power Supply Apparatus 101>

An operation of the power supply apparatus 101 having the aboveconfiguration will now be described using FIGS. 1 and 2. When, forexample, an external signal requesting an operation in which the powerconversion mode of the power supply circuit 10 is set at mode F isinput, the power conversion mode determination processing unit 502 ofthe control unit 50 sets the power conversion mode of the power supplycircuit 10 to mode F. At this time, a power input into the secondinput/output port 60 c is stepped up by a step-up function of theprimary side conversion circuit 20, whereupon the stepped-up power istransmitted to the third input/output port 60 b side by a DC-DCconverter circuit function of the power supply circuit 10, stepped downby a step-down function of the secondary side conversion circuit 30, andthen output from the fourth input/output port 60 d.

Here, a step-up/step-down function of the primary side conversioncircuit 20 will be described in detail. Focusing on the secondinput/output port 60 c and the first input/output port 60 a, theterminal 616 of the second input/output port 60 c is connected to themidpoint 207 m of the primary side first arm circuit 207 via the primaryside first winding 202 a and the primary side first reactor 204 aconnected in series to the primary side first winding 202 a. Respectiveends of the primary side first arm circuit 207 are connected to thefirst input/output port 60 a, and as a result, a step-up/step-downcircuit is attached between the terminal 616 of the second input/outputport 60 c and the first input/output port 60 a.

The terminal 616 of the second input/output port 60 c is also connectedto the midpoint 211 m of the primary side second arm circuit 211 via theprimary side second winding 202 b and the primary side second reactor204 b connected in series to the primary side second winding 202 b.Respective ends of the primary side second arm circuit 211 are connectedto the first input/output port 60 a, and as a result, astep-up/step-down circuit is attached in parallel between the terminal616 of the second input/output port 60 c and the first input/output port60 a. Note that since the secondary side conversion circuit 30 is acircuit having a substantially identical configuration to the primaryside conversion circuit 20, two step-up/step-down circuits are likewiseconnected in parallel between the terminal 622 of the fourthinput/output port 60 d and the third input/output port 60 b. Hence, thesecondary side conversion circuit 30 has an identical step-up/step-downfunction to the primary side conversion circuit 20.

Next, the function of the power supply circuit 10 as a DC-DC convertercircuit will be described in detail. Focusing on the first input/outputport 60 a and the third input/output port 60 b, the primary side fullbridge circuit 200 is connected to the first input/output port 60 a, andthe secondary side full bridge circuit 300 is connected to the thirdinput/output port 60 b. When the primary side coil 202 provided in thebridge part of the primary side full bridge circuit 200 and thesecondary side coil 302 provided in the bridge part of the secondaryside full bridge circuit 300 are magnetically coupled by a couplingcoefficient k_(T), the transformer 400 functions as a center tappedtransformer having a number of windings 1:N. Hence, by adjusting thephase difference φ between the switching period motions of the switchingelements in the primary side full bridge circuit 200 and the secondaryside full bridge circuit 300, power input into the first input/outputport 60 a can be converted and transmitted to the third input/outputport 60 b or power input into the third input/output port 60 b can beconverted and transmitted to the first input/output port 60 a.

FIG. 3 is a view showing a timing chart of ON/OFF switching waveforms ofthe respective arms provided in the power supply circuit 10 resultingfrom control executed by the control unit 50. In FIG. 3, U1 is an ON/OFFwaveform of the primary side first upper arm U1, V1 is an ON/OFFwaveform of the primary side second upper arm V1, U2 is an ON/OFFwaveform of the secondary side first upper arm U2, and V2 is an ON/OFFwaveform of the secondary side second upper arm V2. ON/OFF waveforms ofthe primary side first lower arm /U1, the primary side second lower armN1, the secondary side first lower arm /U2, and the secondary sidesecond lower arm /V2 are inverted waveforms (not shown) obtained byrespectively inverting the ON/OFF waveforms of the primary side firstupper arm U1, the primary side second upper arm V1, the secondary sidefirst upper arm U2, and the secondary side second upper arm V2. Notethat dead time is preferably provided between the respective ON/OFFwaveforms of the upper and lower arms to prevent a through current fromflowing when both the upper and lower arms are switched ON. Further, inFIG. 3, a high level indicates an ON condition and a low level indicatesan OFF condition.

Here, by modifying the respective ON times δ of U1, V1, U2, and V2,step-up/step-down ratios of the primary side conversion circuit 20 andthe secondary side conversion circuit 30 can be modified. For example,by making the respective ON times δ of U1, V1, U2, and V2 equal to eachother, the step-up/step-down ratio of the primary side conversioncircuit 20 can be made equal to the step-up/step-down ratio of thesecondary side conversion circuit 30.

The ON time δ determination processing unit 506 makes the respective ONtimes δ of U1, V1, U2, and V2 equal to each other (respective ON timesδ=primary side ON time δ11=secondary side ON time δ12=time value α) sothat the respective step-up/step-down ratios of the primary sideconversion circuit 20 and the secondary side conversion circuit 30 areequal to each other.

The step-up/step-down ratio of the primary side conversion circuit 20 isdetermined by the duty ratio D, which is a proportion of a switchingperiod T of the switching elements (arms) constituting the primary sidefull bridge circuit 200 occupied by the ON time δ. Similarly, thestep-up/step-down ratio of the secondary side conversion circuit 30 isdetermined by the duty ratio D, which is a proportion of the switchingperiod T of the switching elements (arms) constituting the secondaryside full bridge circuit 300 occupied by the ON time δ. Thestep-up/step-down ratio of the primary side conversion circuit 20 is atransformation ratio between the first input/output port 60 a and thesecond input/output port 60 c, while the step-up/step-down ratio of thesecondary side conversion circuit 30 is a transformation ratio betweenthe third input/output port 60 b and the fourth input/output port 60 d.

Therefore, for example, it is expressed as: the step-up/step-down ratioof the primary side conversion circuit 20=the voltage of the secondinput/output port 60 c/the voltage of the first input/output port 60a=δ11/T=α/T, and the step-up/step-down ratio of the secondary sideconversion circuit 30=the voltage of the fourth input/output port 60d/the voltage of the third input/output port 60 b=δ12/T=α/T. In otherwords, the respective step-up/step-down ratios of the primary sideconversion circuit 20 and the secondary side conversion circuit 30 takeidentical values (=α/T).

Note that the ON time δ in FIG. 3 represents both the ON time δ11 of theprimary side first upper arm U11 and the primary side second upper armV1 and the ON time δ12 of the secondary side first upper arm U2 and thesecondary side second upper arm V2. Further, the switching period T ofthe arms constituting the primary side full bridge circuit 200 and theswitching period T of the arms constituting the secondary side fullbridge circuit 300 are equal times.

Furthermore, a phase difference between U1 and V1 is activated at 180degrees (π), and a phase difference between U2 and V2 is likewiseactivated at 180 degrees (π). The phase difference between U1 and V1 isa time difference between a timing t2 and a timing t6, and the phasedifference between U2 and V2 is a time difference between a timing t1and a timing t5.

Moreover, by changing at least one of a phase difference φu between U1and U2 and a phase difference φv between V1 and V2, the transmittedpower P that is transmitted between the primary side conversion circuit20 and the secondary side conversion circuit 30 can be adjusted. Thephase difference φu is a time difference between the timing t1 and thetiming t2, and the phase difference φv is a time difference between thetiming t5 and the timing t6.

The control unit 50 is an example of a control unit for controlling thetransmitted power P that is transmitted between the primary side fullbridge circuit 200 and the secondary side full bridge circuit 300 viathe transformer 400 by adjusting the phase difference φu and the phasedifference φv.

The phase difference φu is a time difference between switching of theprimary side first arm circuit 207 and switching of the secondary sidefirst arm circuit 307. For example, the phase difference φu is adifference between the turn-on timing t2 of the primary side first upperarm U1 and the turn-on timing t1 of the secondary side first upper armU2. The control unit 50 controls the switching of the primary side firstarm circuit 207 and the switching of the secondary side first armcircuit 307 in an identical-phase with each other (that is, in the Uphase). Similarly, the phase difference φv is a time difference betweenswitching of the primary side second arm circuit 211 and switching ofthe secondary side second arm circuit 311. For example, the phasedifference φv is a difference between the turn-on timing t6 of theprimary side second upper arm V1 and the turn-on timing t5 of thesecondary side second upper arm V2. The control unit 50 controls theswitching of the primary side second arm circuit 211 and the switchingof the secondary side second arm circuit 311 in an identical-phase witheach other (that is, in the V phase).

When the phase difference φu>0 or the phase difference φv>0, thetransmitted power P can be transmitted from the primary side conversioncircuit 20 to the secondary side conversion circuit 30, and when thephase difference φu<0 or the phase difference φv<0, the transmittedpower P can be transmitted from the secondary side conversion circuit 30to the primary side conversion circuit 20. That is, betweenidentical-phase power conversion circuit units of the primary side fullbridge circuit 200 and the secondary side full bridge circuit 300, thetransmitted power P is transmitted from the full bridge circuit of thepower conversion circuit unit including an upper arm that is turned onfirst to the full bridge circuit of the power conversion circuit unitincluding an upper arm that is turned on later.

For example, in FIG. 3, the turn-on timing t1 of the secondary sidefirst upper arm U2 is earlier than the turn-on timing t2 of the primaryside first upper arm U1. Therefore, the transmitted power P istransmitted from the secondary side full bridge circuit 300 includingthe secondary side first arm circuit 307 having the secondary side firstupper arm U2 to the primary side full bridge circuit 200 including theprimary side first arm circuit 207 having the primary side first upperarm U1. Similarly, the turn-on timing t5 of the secondary side secondupper arm V2 is earlier than the turn-on timing t6 of the primary sidesecond upper arm V1. Therefore, the transmitted power P is transmittedfrom the secondary side full bridge circuit 300 including the secondaryside second arm circuit 311 having the secondary side second upper armV2 to the primary side full bridge circuit 200 including the primaryside second arm circuit 211 having the primary side second upper arm V1.

The phase difference φ is a deviation (a time lag) between the switchingtimings of the identical-phase power conversion circuit units of theprimary side full bridge circuit 200 and the secondary side full bridgecircuit 300. For example, the phase difference φu is a deviation betweenthe switching timings of the phases corresponding to the primary sidefirst arm circuit 207 and the secondary side first arm circuit 307, andthe phase difference φv is a deviation between the switching timings ofthe phases corresponding to the primary side second arm circuit 211 andthe secondary side second arm circuit 311.

The control unit 50 typically performs a control in a state that thephase difference φu and the phase difference φv are equal to each other.However, the control unit 50 may also perform the control in a statethat the phase difference φu and the phase difference φv are offset fromone another within a range in which an accuracy required for thetransmitted power P is satisfied. That is, the phase difference φu andthe phase difference φv are typically controlled to be values equal toeach other, whereas if the accuracy required for the transmitted power Pis satisfied, the phase difference φu and the phase difference φv may becontrolled to be values different from each other.

Hence, when, for example, an external signal requesting an operation inwhich the power conversion mode of the power supply circuit 10 is set atmode F is input, the power conversion mode determination processing unit502 selects and sets mode F. The ON time δ determination processing unit506 then sets the ON time δ to define a step-up ratio required when theprimary side conversion circuit 20 is caused to function as a step-upcircuit that steps up the voltage input into the second input/outputport 60 c and outputs the stepped-up voltage to the first input/outputport 60 a. Note that the secondary side conversion circuit 30 functionsas a step-down circuit that steps down the voltage input into the thirdinput/output port 60 b at a step-down ratio defined according to the ONtime δ set by the ON time δ determination processing unit 506, andoutputs the stepped-down voltage to the fourth input/output port 60 d.Further, the phase difference φ determination processing unit 504 setsthe phase difference φ such that the power input into the firstinput/output port 60 a is transmitted to the third input/output port 60b in the desired power transmission amount P.

The primary side switching processing unit 508 performs switchingcontrol on the respective switching elements constituted by the primaryside first upper arm U1, the primary side first lower arm /U1, theprimary side second upper arm V1, and the primary side second lower armN1 to cause the primary side conversion circuit 20 to function as astep-up circuit and to cause the primary side conversion circuit 20 tofunction as a part of a DC-DC converter circuit.

The secondary side switching processing unit 510 performs switchingcontrol on the respective switching elements constituted by thesecondary side first upper arm U2, the secondary side first lower arm/U2, the secondary side second upper arm V2, and the secondary sidesecond lower arm /V2 to cause the secondary side conversion circuit 30to function as a step-down circuit and to cause the secondary sideconversion circuit 30 to function as a part of a DC-DC convertercircuit.

As described above, the primary side conversion circuit 20 and thesecondary side conversion circuit 30 can be caused to function as astep-up circuit or a step-down circuit, and the power supply circuit 10can be caused to function as a bidirectional DC-DC converter circuit.Therefore, power conversion can be performed in all of the powerconversion modes A to L, or in other words, power conversion can beperformed between two input/output ports selected from the fourinput/output ports.

The transmitted power P (also referred to as the power transmissionamount P) adjusted by the control unit 50 in accordance with the phasedifference φ is power transmitted from one of the primary sideconversion circuit 20 and the secondary side conversion circuit 30 tothe other via the transformer 400, and is expressed as

P=(N×Va×Vb)/(π×ω×L)×F(D, φ)   Equation 1

Further, N is a winding ratio of the transformer 400, Va is theinput/output voltage of the first input/output port 60 a, Vb is theinput/output voltage of the third input/output port 60 b, πis pi,ω(=2π×f=2π/T) is an angular frequency of the switching operations of theprimary side conversion circuit 20 and the secondary side conversioncircuit 30, f is a switching frequency of the primary side conversioncircuit 20 and the secondary side conversion circuit 30, T is theswitching period of the primary side conversion circuit 20 and thesecondary side conversion circuit 30, L is an equivalent inductance ofthe magnetic coupling reactors 204, 304 and the transformer 400 relatingto power transmission, and F (D, φ) is a function having the duty ratioD and the phase difference φ as variables and a variable that increasesmonotonically as the phase difference φ increases, independently of theduty ratio D. The duty ratio D and the phase difference φ are controlparameters designed to vary within a range sandwiched betweenpredetermined upper and lower limit values.

The control unit 50 varies the phase difference φ such that a portvoltage Vp of at least one predetermined port of the primary side portsand the secondary side ports converges to a target port voltage Vo,thereby to adjust the transmitted power P. Therefore, even if thecurrent consumed by a load connected to the predetermined portincreases, the control unit 50 can adjust the transmitted power P bychanging the phase difference φ, thereby to prevent the port voltage Vpfrom decreasing with respect to the target port voltage Vo.

For example, the control unit 50 changes the phase difference φ suchthat a port voltage Vp of one port that is the transmission destinationof the transmitted power P of the primary side ports and the secondaryside ports converges to a target port voltage Vo, thereby to adjust thetransmitted power P. Therefore, even if the current consumed by a loadconnected to the port that is the transmission destination of thetransmitted power P increases, the control unit 50 may adjust thetransmitted power P in an increase direction by changing the phasedifference φ to increase, thereby to prevent the port voltage Vp fromdecreasing with respect to the target port voltage Vo.

<Method for Starting Up Power Conversion Apparatus>

FIG. 4 is a flowchart showing an example of a method for starting up thepower supply apparatus 101. The control unit 50 can suppress an inrushcurrent flowing from a power supply at periphery of the power supplycircuit 10 into the respective capacitors by connecting the power supplyat periphery of the power supply circuit 10 to the respective portsafter the capacitors of the respective ports are charged to apredetermined value (for example, a fully charged level) in theprocedure shown in FIG. 4.

FIG. 5 is a timing chart showing an example of operations of the powersupply apparatus 101 when the power supply apparatus 101 is started upby the starting up method shown in FIG. 4. S10, S20, S30, S40, S50 thatare indicated on a time axis of FIG. 5 correspond to timings whenrespective steps S10, S20, S30, S40, S50 of FIG. 4 are executed. In FIG.5, eight pulse waveforms such as U1 indicate ON/OFF waveforms ofrespective arms such as the upper arm U1, and Va (C1), Vb (C2), Vd (C4)indicate voltage waveforms of the port voltages Va, Vb, Vd respectively.The port voltage Va is a voltage of the port 60 a, and is equal to avoltage of the capacitor C1. The port voltage Vb is a voltage of theport 60 b, and is equal to a voltage of the capacitor C2. The portvoltage Vd is a voltage of the port 60 d, and is equal to a voltage ofthe capacitor C4.

In step S10 of FIG. 4, as shown in FIG. 6, the capacitor C1 that isconnected to the port 60 a is charged by the control unit 50 via thecenter tap 202 m with the power Pc that is input to the port 60 c fromthe power supply 62 c that is connected to the port 60 c. When thecapacitor C1 is charged in step S10, the control unit 50 can suppress amagnitude of an inrush current flowing to the capacitor C1 from thepower supply 62 c via the center tap 202 m by causing at least one ofthe upper arm U1 and the upper arm V1 to operate in an active region.

The active region (also referred to as “an activated region”) is anoperation region in which a switching element is conductive with apredetermined resistance value R_(T) or more when a gate voltage of theswitching element is within a range in which it is equal to or higherthan a gate threshold voltage and is equal to or lower than apredetermined voltage value Vth. The predetermined voltage value Vth isa voltage value that is lower than the gate voltage in a steady stateafter starting up of the power supply apparatus 101 is completed, forexample, a voltage value during a mirror period before the switchingelement enters a saturation region.

When the switching element operates in the active region, the switchingelement is in a state where it is conductive with the resistance valueR_(T) or more. The active region may also be referred to as a half-ONstate indicating an intermediate state of ON and OFF states of theswitching element. The active region contains an amplifying operationregion in which a resistance value of the switching element decreaseslinearly and a current flowing to the switching element increaseslinearly as the gate voltage or a base current increases.

That is, the control unit 50 causes the switching element to function asa current limiting resistor with a variable resistance value byadjusting the gate voltage or the base current of the switching elementto a value for operating in the active region during an extremely shortperiod of charging the capacitor when the power supply apparatus 101 isstarted up.

Note that, as for a target value of a resistance component of theswitching element or a current flowing in the switching element, thatis, a target value of the gate voltage or the base current, it may bedetermined according to a heat-resistant specification, an allowablecurrent amount, and the like of the switching element, for example, inonly consideration of heat generation of the switching element thatoperates in the active region. Specifically, the target value of thegate voltage or the base current may be determined such that temperaturethat is estimated from a power consumption of the switching element, athermal resistance of a package of the switching element, and the likeis equal to or lower than heat-resistant specification temperature.

Therefore, in FIG. 6, a charging current supplied to the capacitor C1via the center tap 202 m from the power supply 62 c is suppressed by theupper arm U1 or V1 that operates in the active region. Thus, by at leastone of the upper arm U1 and the upper arm V1 operating in the activeregion, it is possible to suppress the magnitude of the inrush currentflowing to the capacitor C1 from the power supply 62 c via the centertap 202 m.

FIGS. 5 and 6 show the case where, in step S10 from a timing t11 to atiming t12, the control unit 50 causes only the upper arm U1 to operatein the active region and switches all the remaining seven arms such asthe upper arm V1 OFF. By the control unit 50 causing only the upper armU1 to operate in the active region, as shown in FIG. 6, the chargingcurrent supplied to the capacitor C1 via the center tap 202 m from thepower supply 62 c flows in a path that goes through the winding 202 a,the reactor 204 a and the upper arm U1.

In step S10, the control unit 50 may also cause the upper arm U1 and theupper arm V1 both to operate in the active region. By the upper arm U1and the upper arm V1 both operating in the active region, it is possibleto shorten a time for charging the capacitor C1 while a currentlimitation is effected. Thus, it is possible to suppress the inrushcurrent of the capacitor C1 and shorten the time until the starting upof the power supply apparatus 101 is completed.

Note that, a configuration not having the diodes 81, 83 in the upperarms U1, V1 is effective in suppression of the inrush current of thecapacitor C1. However, even in a configuration having the diodes 81, 83in the upper arms U1, V1, the control unit 50 may also suppress theinrush current of the capacitor C1 by causing the upper arm U1 or theupper arm V1 to operate in the active region. A preferred example of theconfiguration having the diodes 81, 83 in the upper arms U1, V1 will bedescribed later.

Further, in FIG. 1, although a switch 93 is inserted between the powersupply 62 c and the terminal 616 of the port 60 c, the switch 93 may beomitted. The switch 93 is an example of a unit for permitting powerinput and output between the power supply 62 c and the port 60 c. Forexample, when the switch 93 is turned on by the control unit 50, thepower input and output is permitted, and when the switch 93 is turnedoff by the control unit 50, the power input and output is inhibited. Thecontrol unit 50, for example, turns on the switch 93 before the startingup timing t11 (see FIG. 5) of the power supply apparatus 101.

In step S20 of FIG. 4, the control unit 50 determines whether thecapacitor C1 is being charged until the port voltage Va is detected tobe a specified predetermined value X1 or more. The predetermined valueX1 is, for example, a detected value of the port voltage Vc detected bythe sensor unit 70, and is a threshold value that is substantially equalto a supply voltage of the power supply 62 c (for example, 12V).

The control unit 50 continues the processing of step S10 until the portvoltage Va is detected by the sensor unit 70 to be the predeterminedvalue X1 or more. The processing of step S30 is performed when the portvoltage Va is detected by the sensor unit 70 to be the predeterminedvalue X1 or more.

In step S30 of FIG. 4, the control unit 50 controls the four arms of thesecondary side full bridge circuit 300 to transmit the transmitted powerP to the secondary side full bridge circuit 300 (see FIG. 5) whilecontrolling the four arms of the primary side full bridge circuit 200 toincrease the port voltage Va from the predetermined value X1 to aspecified predetermined value X2. The predetermined value X2 is a valuegreater than the predetermined value X1, for example, a threshold valuethat is equal to a normal voltage of the port 60 a (for example, 48Vcorresponding to the voltage system of the load 61 a).

The control unit 50 can charge the capacitor C2 that is connected to theport 60 b and the capacitor C4 that is connected to the port 60 d at thesame time by adjusting the phase difference φ to transmit thetransmitter power P from the primary side full bridge circuit 200 to thesecondary side full bridge circuit 300. Further, although the phasedifference φ is not clearly shown in FIG. 5, the control unit 50 turnson and off the eight arms as shown in FIG. 3 during step S30 from atiming t13 to a timing t14, so as to transmit the transmitted power Pcorresponding to the phase difference φ.

FIG. 7 shows a direction and a path of the charging current of thecapacitors C1, C2, C4 when the upper arm U1, the lower arm N1, the upperarm U2 and the lower arm /V2 are turned on and the remaining four armsare turned off during a period from the timing t13 to the timing t14 inFIG. 5. FIG. 8 shows a direction and a path of the charging current ofthe capacitors C1, C2, C4 when the upper arm V1, the lower arm /U1, theupper arm V2 and the lower arm /U2 are turned on and the remaining fourarms are turned off during the period from the timing t13 to the timingt14 in FIG. 5. The control unit 50 controls the eight arms to be turnedon and off during the period from the timing t13 to the timing t14, sothat states shown in FIGS. 7 and 8 are alternately repeated.

In step S30, the control unit 50 controls the ON time δ of each arm ofthe primary side full bridge circuit 200 with the duty ratio D, therebyto step up the power Pc that is input to the port 60 c and output thestepped up power Pa to the port 60 a. The control unit 50 graduallyincreases the port voltage Va with the stepped up power Pa, from theport voltage Va is detected by the sensor unit 70 to be thepredetermined value X1 or more until the port voltage Va is detected bythe sensor unit 70 to be the predetermined value X2 or more (see FIG.5). The control unit 50 may also switch the four arms of the primaryside full bridge circuit 200 that are turned on with the duty ratio D ONcompletely in the saturation region when raising the port voltage Vafrom the predetermined value X1 to the predetermined value X2

The saturation region is referred to an operation region in which theswitching element is conductive with a value less than the predeterminedresistance value R_(T). When the switching element is turned oncompletely in the saturation region, the switching element is in a statewhere it is conductive with a value less than the resistance valueR_(T.)

The control unit 50 also controls the ON time δ of the four arms of thesecondary side full bridge circuit 300 with the same duty ratio D asthat of each arm of the primary side full bridge circuit 200, whenraising the port voltage Va from the predetermined value X1 to thepredetermined value X2 in step S30, to transmit the transmitted power P.When turning on one upper arm of the secondary side full bridge circuit300, as shown in FIG. 7 or 8, the control unit 50 turns on one lower armthat is arranged in a phase opposite to that of the one upper arm.

In step S30, the control unit 50 charges the capacitor C2 with thetransmitted power P that is transmitted via the transformer 400 whileperforming a step up operation of stepping up the power Pc that is inputto the port 60 c and outputting the stepped up power Pa to the port 60a. When charging the capacitor C2 with the transmitted power P that istransmitted while the step up operation is performed, the control unit50 can suppress the magnitude of the inrush current flowing to thecapacitor C2 based on the transmitted power P by causing at least one ofthe upper arm U2 and the upper arm V2 to operate in the active region.Further, it is possible to suppress the magnitude of the inrush currentflowing to the capacitor C2 from the power supply 62 b via the port 60b, even if the power supply 62 b is connected to the port 60 b through aswitch 92, as the capacitor C2 can be pre-charged before the powersupply 62 b is connected to the port 60 b through the switch 92.

Note that, a configuration not having the diodes 87, 85 in the upperarms U2, V2 is effective in suppression of the inrush current of thecapacitor C2. However, even in a configuration having the diodes 87, 85in the upper arms U2, V2, the control unit 50 may also suppress theinrush current of the capacitor C2 by causing the upper arm U2 or theupper arm V2 to operate in the active region. A preferred example of theconfiguration having the diodes 87, 85 in the upper arms U2, V2 will bedescribed later.

The switch 92 is inserted between the power supply 62 b and the terminal618 of the port 60 b. The switch 92 is an example of a unit forpermitting power input and output between the power supply 62 b and theport 60 b. For example, when the switch 92 is turned on by the controlunit 50, the power input and output is permitted, and when the switch 92is turned off by the control unit 50, the power input and output isinhibited.

Since the control unit 50 allows a power supplied by the power supply 62b to be input from the port 60 b, for example, when the port voltage Vbis detected by the sensor unit 70 to be a specified predetermined valueX3 or more, the switch 92 is turned on. The predetermined value X3 is,for example, a threshold value that is equal to a normal voltage of theport 60 b (for example, 288V corresponding to the voltage system of theload 61 b or the power supply 62 b).

Similarly, in step S30, the control unit 50 charges the capacitor C4with the transmitted power P that is transmitted via the transformer 400while performing a step up operation of stepping up the power Pc that isinput to the port 60 c and outputting the stepped up power Pa to theport 60 a. When charging the capacitor C4 with the transmitted power Pthat is transmitted while the step up operation is performed, thecontrol unit 50 can suppress the magnitude of the inrush current flowingto the capacitor C4 based on the transmitted power P by causing at leastone of the lower arm /U2 and the lower arm /V2 to operate in the activeregion. Further, it is possible to suppress the magnitude of the inrushcurrent flowing to the capacitor C4 from the power supply 62 d via theport 60 d, even if the power supply 62 d is connected to the port 60 dthrough a switch 94, as the capacitor C4 can be pre-charged before thepower supply 62 d is connected to the port 60 d through the switch 94.

Note that, a configuration not having the diodes 88, 88 in the lowerarms /U2, /V2 is effective in suppression of the inrush current of thecapacitor C4. However, even in a configuration having the diodes 88, 86in the lower arms /U2, /V2, the control unit 50 may also suppress theinrush current of the capacitor C4 by causing the lower arm /U2 or thelower arm /V2 to operate in the active region. A preferred example ofthe configuration having the diodes 88, 86 in the lower arms /U2, /V2will be described later.

The switch 94 is inserted between the power supply 62 d and the terminal622 of the port 60 d. The switch 94 is an example of a unit forpermitting power input and output between the power supply 62 d and theport 60 d. For example, when the switch 94 is turned on by the controlunit 50, the power input and output is permitted, and when the switch 94is turned off by the control unit 50, the power input and output isinhibited.

Since the control unit 50 allows a power supplied by the power supply 62d to be input from the port 60 d, for example, when the port voltage Vdis detected by the sensor unit 70 to be a specified predetermined valueX4 or more, the switch 94 is turned on. The predetermined value X4 is,for example, a threshold value that is equal to a normal voltage of theport 60 d (for example, 72V corresponding to the voltage system of theload 61 d or the power supply 62 d).

Further, in step S30, the control unit 50 may also switch the lower arms/U2, /V2 of the secondary side full bridge circuit 300 that are turnedon with the duty ratio D ON completely in the saturation region (seeFIG. 5). If there are the diodes 88, 86, it is also possible to turn offthe lower arms /U2, /V2 always.

Further, the control unit 50 may also charge the capacitor C2 or C4 withthe transmitted power P that is transmitted to the secondary side fullbridge circuit 300 while the step up operation of the primary side fullbridge circuit 200 is performed after the timing t14 that the portvoltage Va gradually increases to reach the predetermined value X2 withthe stepped up power Pa. However, the control unit 50 can shorten thetime until a timing t15 that the starting up of the power supplyapparatus 101 is completed by charging the capacitor C2 or C4 with thetransmitted power P that is transmitted during the port voltage Vagradually increases with the stepped up power Pa as shown in FIG. 5 (theperiod from the timing t13 to the timing t14).

Further, in step S30, for example, the control unit 50 may alsogradually increase the duty ratio D of time for which the four arms ofthe primary side full bridge circuit 200 are tuned on as shown in FIG.5, and charge the capacitor C1 with the stepped up power Pa. The controlunit 50 can improve the effect of suppressing the magnitude of theinrush current flowing to the capacitor C1 via the center tap 202 m fromthe power supply 62 c by gradually increasing the duty ratio D andcharging the capacitor C1 with the stepped up power Pa.

Similarly, in step S30, for example, the control unit 50 may alsogradually increase the duty ratio D of time for which the two upper armsV2, U2 of the secondary side full bridge circuit 300 operate in theactive region, and charge the capacitor C2 with the transmitted power P.The control unit 50 can improve the effect of suppressing the magnitudeof the inrush current flowing to the capacitor C2 based on thetransmitted power P by gradually increasing the duty ratio D andcharging the capacitor C2 with the transmitted power P.

Similarly, in step S30, for example, the control unit 50 may alsogradually increase the duty ratio D of time for which the two lower arms/V2, /U2 of the secondary side full bridge circuit 300 operate in theactive region, and charge the capacitor C4 with the transmitted power P.The control unit 50 can improve the effect of suppressing the magnitudeof the inrush current flowing to the capacitor C4 based on thetransmitted power P by gradually increasing the duty ratio D andcharging the capacitor C4 with the transmitted power P.

FIG. 9 is a diagram showing an example of an ON/OFF waveform of the armswhen the duty ratio D is constant, and an example of an ON/OFF waveformof the arms when the duty ratio D gradually increases.

In FIG. 9, the ON/OFF waveform when the duty ratio D is constant showsthe case where the control unit 50 performs a normal control ofadjusting the transmitted power P or the duty ratio D to make a feedbackvalue of the port voltage Vp of each port coincide with the target portvoltage Vo. In the case where the voltage of the capacitor connected toeach port is very low relative to the target port voltage Vo when thepower supply apparatus 101 is started up, the control unit 50 increasesthe duty ratio D to the maximum extent from start of the feedbackcontrol so that the feedback value of the port voltage Vp rapidlycoincides with the target port voltage Vo. Therefore, it is likely toincrease the inrush current flowing to the capacitor.

In contrast, the control unit 50 can improve the effect of suppressingthe magnitude of the inrush current flowing to the capacitor bygradually increasing the duty ratio D at a predetermined increasing rateinstead of performing the feedback control of making the feedback valueof the port voltage Vp coincide with the target port voltage Vo.Alternatively, a time required to charge the capacitor is pre-derivedanalytically or experimentally according to a capacity of the capacitor,and the control unit 50 gradually increases the duty ratio D such thatthe pre-derived time reaches a stable target duty ratio, which canimprove the effect of suppressing the inrush current of the capacitor.

In step S40 of FIG. 4, the control unit 50 allows the power supplied bythe power supply 62 b to be input from the port 60 b when the portvoltage Va is detected by the sensor unit 70 to be the predeterminedvalue X2 or more and the port voltage Vb is detected by the sensor unit70 to be the predetermined value X3 or more (step S50). Therefore, it ispossible to suppress the inrush current flowing to the capacitor C2 fromthe power supply 62 b. Similarly, the control unit 50 allows a powersupplied by the power supply 62 d to be input from the port 60 d whenthe port voltage Va is detected by the sensor unit 70 to be thepredetermined value X2 or more and the port voltage Vd is detected bythe sensor unit 70 to be the predetermined value X4 or more (step S50).Therefore, it is possible to suppress the inrush current flowing to thecapacitor C4 from the power supply 62 d.

In step S50, for example, the control unit 50 the normal control ofadjusting the transmitted power P or the duty ratio D to make thefeedback value of the port voltage Vp of each port coincide with thetarget port voltage Vo after the timing t15 that is shown in FIG. 5. Onthe other hand, if the condition of step S40 is not satisfied, thecontrol unit 50 continues the processing of step S30 of charging thecapacitor C2 or C4.

FIG. 10 shows a preferred example of a configuration having a diode inthe upper arm, and shows a configuration having diodes 87, 85 in theupper arms U2, V2 of the secondary side. In the case of FIG. 10, thesecondary side full bridge circuit 300 includes a U phase upper arm inwhich the upper arm U2 and an upper arm U22 are connected in series, anda V phase upper arm in which the upper arm V2 and an upper arm V22 areconnected in series. The upper arm U2 is an example of a first switchingelement having a first diode 87 provided in parallel with a directionfor charging the capacitor C2 as a forward direction, and the upper U22is an example of a second switching element having a second diode 187provided in parallel with a direction opposite to the direction of thefirst diode 87 as the forward direction. Similarly, the upper arm V2 isan example of the first switching element having the first diode 85provided in parallel with the direction for charging the capacitor C2 asthe forward direction, and the upper arm V22 is an example of the secondswitching element having the second diode 185 provided in parallel witha direction opposite to the direction of the first diode 85 as theforward direction.

When charging the capacitor C2 with the transmitted power P, the controlunit 50 can suppress the inrush current of the capacitor C2 flowingthrough the upper arm

U22 or V22 via the diode 85 or 87 by causing the upper arm U22 or theupper arm V22 to operate in the active region in a state where the upperarms U2 and V2 are turned off

Further, the configuration of FIG. 10 is also applicable to the casewhere there are diodes 81, 83 in the primary side upper arms U1, V1. Thedescription of the primary side upper arm is incorporated by withreference to the above description of the secondary side upper arm.

FIG. 11 shows a preferred example of a configuration having a diode inthe lower arm, and shows a configuration having diodes 88, 86 in thelower arms /U2, /V2 of the secondary side. In the case of FIG. 11, thesecondary side full bridge circuit 300 includes a U phase lower arm inwhich the lower arm /U2 and an lower arm /U22 are connected in series,and a V phase lower arm in which the lower arm /V2 and an lower arm /V22are connected in series. The lower arm /U2 is an example of a thirdswitching element having a third diode 88 provided in parallel with adirection for charging the capacitor C4 as a forward direction, and thelower /U22 is an example of a fourth switching element having a fourthdiode 188 provided in parallel with a direction opposite to thedirection of the third diode 88 as the forward direction. Similarly, thelower arm /V2 is an example of the third switching element having thethird diode 86 provided in parallel with the direction for charging thecapacitor C4 as the forward direction, and the lower arm /V22 is anexample of the fourth switching element having the fourth diode 186provided in parallel with a direction opposite to the direction of thethird diode 86 as the forward direction.

When charging the capacitor C4 with the transmitted power P, the controlunit 50 can suppress the inrush current of the capacitor C4 flowingthrough the lower arm /U22 or /V22 via the diode 88 or 86 by causing thelower arm /U22 or the lower arm /V22 to operate in the active region ina state where the lower arms /U2 and /V2 are turned off

Further, the configuration of FIG. 11 is also applicable to the casewhere there are diodes 82, 84 in the primary side lower arms /U1, /V1.The description of the primary side lower arm is incorporated by withreference to the above description of the secondary side lower arm.

FIG. 12 is a diagram showing that depending on current or temperature inany arm of the primary side full bridge circuit 200 or the secondaryside full bridge circuit 300, the control unit 50 interrupts theoperation of causing the arm to operate in the active region. At atiming when the current or temperature of the arm that is operating inthe active region is detected by the sensor unit 70 to be apredetermined upper limit value or more, the control unit 50 may alsoturn off temporarily a driving command value of the arm, and cause thearm to operate in the active region again after a predetermined time haselapsed since it was turned off temporarily. Therefore, it is possibleto prevent a failure of the arm due to an overcurrent or overheating.

An embodiment of the power conversion apparatus and the method forstarting up the same was described above, but the invention is notlimited to the above embodiment, and various amendments andimprovements, such as combining or replacing the above embodiment eitherpartially or wholly with another embodiment, may be implemented withinthe scope of the invention.

For example, in the above embodiment, a MOSFET, which is a semiconductorelement subjected to an ON/OFF operation, was cited as an example of theswitching element. However, the switching element may be a voltagecontrol type power element using an insulating gate such as an insulatedgate bipolar transistor (IGBT) or a MOSFET, or a bipolar transistor, forexample.

Further, a power supply may be connected to the first input/output port60 a. Further, a power supply may be connected to the third input/outputport 60 b, and a power supply need not be connected to the fourthinput/output port 60 d. Further, a power supply need not be connected tothe third input/output port 60 b, and a power supply may be connected tothe fourth input/output port 60 d.

Further, the present invention is suitable for a power conversionapparatus that has a plurality of, at least three or more, input/outputports and is capable of converting power between any two input/outputports of the plurality of, at least three or more, input/output ports.For example, the present invention is also suitable for the power supplyapparatus configured to not include any one input/output port of thefour input/output ports as illustrated in FIG. 1.

Further, in the above description, the primary side may be defined asthe second side, and the second side may be defined as the primary side.In the above description, although a case that the transmitted power Pis transmitted to the primary side port from the secondary side port hasbeen illustrated as an example, the above description can be applied tothe case that the transmitted power P is transmitted to the secondaryside port from the primary side port.

What is claimed is:
 1. A power conversion apparatus comprising: atransformer; a primary side full bridge circuit that is provided on aprimary side of the transformer; a first port that is connected to theprimary side full bridge circuit; a second port that is connected to acenter tap of the primary side of the transformer; a secondary side fullbridge circuit that is provided on a secondary side of the transformer;a third port that is connected to the secondary side full bridgecircuit; and a control unit that is configured to cause an upper arm ofthe secondary side full bridge circuit to operate in an active region ina case where a capacitor that is connected to the third port is chargedwith a transmitted power that is transmitted to the secondary side fullbridge circuit via the transformer from the primary side full bridgecircuit when a power of the second port is stepped up and the stepped uppower is output to the first port.
 2. The power conversion apparatusaccording to claim 1, wherein the control unit is configured togradually increase a duty ratio of time for which the upper arm of thesecondary side full bridge circuit operates in the active region, and tocharge the capacitor that is connected to the third port with thetransmitted power.
 3. The power conversion apparatus according to claim1, wherein the secondary side full bridge circuit includes the upper armin which a first switching element having a first diode provided inparallel with a direction for charging the capacitor as a forwarddirection and a second switching element having a second diode providedin parallel with a direction opposite to the direction of the firstdiode as a forward direction are connected in series, and the controlunit is configured to cause the second switching element to operate inthe active region, and to charge the capacitor that is connected to thethird port with the transmitted power.
 4. The power conversion apparatusaccording to claim 1, wherein the control unit is configured to allow apower to be input from the third port when a voltage of the capacitorthat is connected to the third port is equal to or greater than apredetermined value.
 5. The power conversion apparatus according toclaim 1, further comprising a fourth port that is connected to a centertap of the secondary side of the transformer, wherein the control unitis configured to charge a capacitor that is connected to the fourth portwith the transmitted power.
 6. The power conversion apparatus accordingto claim 5, wherein the control unit is configured to cause a lower armof the secondary side full bridge circuit to operate in the activeregion when the capacitor that is connected to the fourth port ischarged with the transmitted power.
 7. The power conversion apparatusaccording to claim 6, wherein the control unit is configured togradually increase a duty ratio of time for which the lower arm of thesecondary side full bridge circuit operates in the active region, and tocharge the capacitor that is connected to the fourth port with thetransmitted power.
 8. The power conversion apparatus according to claim6, wherein the secondary side full bridge circuit includes the lower armin which a third switching element having a third diode provided inparallel with a direction for charging the capacitor as a forwarddirection and a fourth switching element having a fourth diode providedin parallel with a direction opposite to the direction of the thirddiode as a forward direction are connected in series, and the controlunit is configured to cause the fourth switching element to operate inthe active region, and to charge the capacitor that is connected to thefourth port with the transmitted power.
 9. The power conversionapparatus according to claim 5, wherein the control unit is configuredto allow a power to be input from the fourth port when a voltage of thecapacitor that is connected to the fourth port is equal to or greaterthan a predetermined value.
 10. The power conversion apparatus accordingto claim 1, wherein the control unit is configured to cause an upper armof the primary side full bridge circuit to operate in the active regionwhen a capacitor that is connected to the first port is charged by apower supply that is connected to the second port via the center tap ofthe primary side.
 11. The power conversion apparatus according to claim10, wherein the control unit is configured to gradually increase avoltage of the capacitor that is connected to the first port with thestepped up power from detecting that the voltage of the capacitor thatis connected to the first port is equal to or greater than a firstthreshold value until detecting that the voltage of the capacitor thatis connected to the first port is equal to or greater than a secondthreshold value that is greater than the first threshold value.
 12. Thepower conversion apparatus according to claim 11, wherein the controlunit is configured to gradually increase a duty ratio of time for whichan arm of the primary side full bridge circuit is turned on, and tocharge the capacitor that is connected to the first port with thestepped up power.
 13. The power conversion apparatus according to claim1, wherein the control unit is configured to charge the capacitor thatis connected to the third port with the transmitted power that istransmitted during a period of gradually increasing a voltage of thefirst port with the stepped up power.
 14. The power conversion apparatusaccording to claim 1, wherein the control unit is configured tointerrupt, according to current or temperature of an arm of the primaryside full bridge circuit or current or temperature of an arm of thesecondary side full bridge circuit, an operation of the arm in theactive region.
 15. A method for starting up a power conversionapparatus, which includes a transformer; a primary side full bridgecircuit that is provided on a primary side of the transformer; a firstport that is connected to the primary side full bridge circuit; a secondport that is connected to a center tap of the primary side of thetransformer; a secondary side full bridge circuit that is provided on asecondary side of the transformer; and a third port that is connected tothe secondary side full bridge circuit, the method for starting up thepower conversion apparatus comprising: causing an upper arm of thesecondary side full bridge circuit to operate in an active region in acase where a capacitor that is connected to the third port is chargedwith a transmitted power that is transmitted to the secondary side fullbridge circuit via the transformer from the primary side full bridgecircuit when a power of the second port is stepped up and the stepped uppower is output to the first port.